Commonly, it is known that by forming a film on the surface of a solid material in plasma or by injecting ions, the solid surface characteristics can be improved. A film formed using plasma that includes metal or nonmetal ions strengthens the abrasion/corrosion resistance of the solid surface, and it is useful as a protective film, an optical thin film, a transparent electroconductive film, or such. In particular, a carbon film using carbon plasma comprises an amorphous conglomerate of the diamond and the graphite structures, and its utility value is high as a diamond like carbon film (referred to as a “DLC film”).
As a method for generating plasma including metal or nonmetal ions, there is a vacuum arc plasma technique. Vacuum arc plasma is plasma formed by an electric arc discharge generated between the cathode and the anode, wherein the cathode material evaporates from a cathode spot existing on the cathode surface, and said plasma is formed from this cathode-vaporized material. In addition, when a reactive gas is introduced as the atmosphere gas, the reactive gas is ionized simultaneously. An inert gas (referred to as a “noble gas”) may be introduced along with said reactive gas, and also, said inert gas can be introduced instead of said reactive gas. A surface treatment can be done by using such plasma for a thin film formation on a solid surface or an injection of ion.
Normally, in a vacuum arc discharge, vacuum arc plasma constituent particles such as cathode material ions, electrons, and cathode material neutral particles (atoms and molecules) are ejected from the cathode spot, and at the same time, cathode material particles called droplets with size from less than submicron to several hundred microns (0.01-1000 μm) are also ejected. However, what becomes a problem in a surface treatment such as film formation is generation of the droplets. When these droplets adhere to the surface of the object to be treated, the uniformity of the film formed on the surface of the object to be treated is lost, and the film becomes a defective product.
As a method to solve the problem of droplets, there is a magnetic filter method (P. J. Martin, R. P. Netterfield and T. J. Kinder, Thin Solid Films 193/194 (1990)77) (Non-Patent Document 1). In this magnetic filter method, vacuum arc plasma is transported to a processing portion through a curved droplet collecting duct. According to this method, the droplets which were generated are adhered and captured (collected) on the duct inner circumferential wall, and a plasma stream that nearly does not contain droplets is obtained at the duct outlet. Also, a curved magnetic field is formed by magnets arranged along the duct. The plasma stream is bent by this curve magnetic field, and it is configured so that the plasma is guided efficiently to the plasma processing portion.
A plasma arc processing apparatus having a droplet collecting portion is disclosed in the Japanese Patent Laid-Open No. 2002-8893 bulletin (Patent Document 1). FIG. 12 is a schematic configuration diagram of a conventional plasma arc processing apparatus. At plasma generating portion 102, an electric spark is generated between cathode 104 and trigger electrode 106, a vacuum arc is generated between cathode 104 and anode 108, and plasma 109 is generated. To plasma generating portion 102, power supply 110 for generating electric spark and vacuum arc discharge is connected, and plasma stabilizing magnetic field generators 116a, 116b for stabilizing plasma 109 are arranged. Plasma 109 is guided from plasma generating portion 102 to plasma processing portion 112, and object to be treated 114 that is placed in plasma processing portion 112 is subjected to a surface treatment by said plasma 109. Also, a reactive gas is introduced as necessary through gas introduction system Gt connected to plasma processing portion 112, and the reactant gas and the plasma stream are exhausted by gas exhaust system Gh.
Plasma 109 ejected from plasma generating portion 102 is bent in the shape of a T by a magnetic field to a direction not facing plasma generating portion 102, and is flowed into plasma processing portion 112. At the position facing plasma generating portion 102, droplet collecting portion 120 is arranged, on which cathode material particles (droplets) 118, produced from the cathode as a byproduct at the time of generation of plasma 109, are sampled. Therefore, droplets 118 that are not affected by the magnetic field advance to droplet collecting portion 120 to be collected, and droplets 118 are prevented from infiltrating plasma processing portion 112. As a specific droplets collecting means, for example, an adhesion and collecting of droplets that do not arrive at the plasma processing portion, using a baffle set up in the plasma duct wall, is disclosed in the Japanese Patent Laid-Open No. 2002-105628 bulletin (Patent Document 2).
[patent document 1] Japanese Patent Laid-Open No. 2002-8893 bulletin
[patent document 2] Japanese Patent Laid-Open No. 2002-105628 bulletin
[non-patent document 1] P. J. Martin, R. P. Netterfield and T. J. Kinder, Thin Solid Films 193/194 (1990)77